78 Journal of Comparative Neurology 



bundles, one from the dorsal and the other from the ventral 

 angle of the cephalic margin of the lobes. Between these roots 

 the substance of the lobe curves slightly cephalad ; the ventral 

 surface is similar in outline to the dorsal. 



Prosencephal. — The cerebrum of Chelydra is not well devel- 

 oped even for a reptilian type. From the dorsum the outline 

 of each hemisphere is irregularly ellipsoidal. The mesal sur- 

 faces are closely approximated for their cephalic third but they 

 divaricate caudad from that point. The caudal projection of the 

 hemispheres overlaps and almost completely hides the dien- 

 cephal from the dorsal aspect, and also slightly overlaps the 

 pregemina. On the cephalic portion of each hemisphere, origin- 

 ating at the meso-cephalic margin, at the level of the dorsal sur- 

 face of the olfactory lobe, is a furrow that extends latero-caudad 

 around the lateral margin of the hemispheres. This feature I 

 have not observed in any other reptile. From the lateral aspect 

 (Fig. 3) the hemispheres have a broadly ellipsoidal outline. 

 From this side is shown the slightly lobed structure of the hem- 

 ispheres ; the occipito-basal lobe of Herrick projects ventrad 

 from the caudal portion of the hemispheres, overlapping from 

 the lateral aspect the diencephal and the cephalic portion of the 

 pregemina. These lobes are more distinctly shown from the 

 ventral view (Fig. 2). From this aspect three ventral projec- 

 tions of the surface are shown. The general outline of the hem- 

 ispheres from the ventral aspect is the same as from the dorsal, 

 but the greatest lateral diameter of the cerebrum is a line pass- 

 ing through the hemispheres near their dorsal surface, the out- 

 line of a transection of the cerebrum being cuneiform with the 

 apex of the wedge ventrad. 



Diencephal. — The diencephal is almost entirely hidden by 

 the overlapping cerebrum, nothing being visible on the dorsal 

 surface, but the dorsal outgrowth, which has been described 

 above and is shown in the figures. The ventral surface is formed 

 mainly by the infundibulum, to which is attached the hypo- 

 physis. 



MesencephaL — The mesencephal is prominent in the dorsal 

 aspect of the brain, the pregemina, as is usual in reptiles, being 



